The present invention relates to a process of interesterification reaction of fats, wherein the rate of interesterification reaction is increased and the reaction is continued constantly at a high rate for a long time, and more specifically, to a form of the lipase enzyme which exhibits a catalytic action to the interesterification reaction, which is, to a dry cell which contains the lipase enzyme in itself.
Hitherto, there have been used an alkaline metal, and the alkoxylate and the hydroxyl compound thereof as a catalyst in the interesterification reaction of the fats. But those catalysts do not have the specificity to react specific positions of glycerides. Recently, the lipase enzyme is used as a catalyst in the reaction, e.g. when the lipase enzyme acts on a mixture of the fat and the fatty acid, the interesterification (also known as transesterification) reaction is carried out at a specific position according to the characteristics of the enzyme. By using such a method, various fatty acids were subjected to the interesterification according to the various purposes [cf. Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 104506/1977, Japanese Examined Patent Publications (Tokkyo Kokoku) No. 6480/1982, No. 27159/1982 and No. 28519/1982]. However, in case of using an enzyme as a catalyst, which does not exhibit activity until dissolved in water or in the presence of water, on a substrate (a reactant) immiscible with water such as a fat or a fatty acid, there are some problems as follows:
(1) For the purpose of increasing a rate of contact between the substrate and the enzyme, it is desirable to add the enzyme directly to the substrate. However, the enzyme is rapidly inactivated in the fats or organic solvent unless it is protected in some manner. In the above-mentioned Patent Publications, a method is disclosed, wherein the enzyme is adsorbed to a carrier such as an adsorbent to prevent inactivation. But the enzyme rapidly loses its activity, as soon as it is desorbed from the carrier.
(2) When there is too great and amount of water in the vicinity of the enzyme, the hydrolysis (saponification) reaction becomes dominant and the interesterification reaction hardly proceeds 0n the contrary, when the amount of water is too small, though the interesterification reaction certainly proceeds, a rate of reaction is very slow and the enzyme loses its activity. There are described the amounts of water suitable for the interesterification reaction of 0.2 to 1.0% by weight in Japanese Unexamined Patent Publication No. 104506/1977, 0.005 to 0.18% by weight in Japanese Examined Patent Publication No. 27159/1982 and 0.01 to 0.20% by weight in Japanese Examined Patent Publication No. 28519/1982, respectively. There is also disclosed in Japanese Examined Patent Publication No. 6480/1982 that the interesterification reaction can be carried out without hydrolysis when lower alcohols of 2 or 3 hydroxyl groups are used in place of water. However, according to the inventors' experience, the rate of reaction is small in those methods and they are poor in practical use.
(3) With respect to the method, wherein the enzyme is adsorbed to a carrier of an adsorbent, reactants can hardly diffuse to the enzyme on the carrier, and especially, the enzyme adsorbed into fine pores of the carrier substantially cannot take part in the reaction, and therefore an amount of the effective enzyme is decreased. Such a tendency becomes more striking as a more hydrophilic carrier is used.
As mentioned above, in case of conducting the interesterification reaction, wherein the lipase enzyme which exhibits an activity in an aqueous system is reacted as a catalyst with an oily reactant, it is necessary not to inactivate the enzyme, to control an amount of water in the vicinity of the enzyme in a suitable amount and not to decrease the rate of contact between the enzyme and the reactant Every Patent Publication described above mainly pays attention to the above-mentioned problem (2) only and has little regard for the problems (1) and (3). However, the problems (1) and (3) are very important subjects for the interesterification system, wherein the reactant and the enzyme consist in the different phases, respectively, and the enzyme is under a condition that it is easy to lose its activity.
It is an object of the present invention to solve the above-mentioned problems and to carry out the interesterification reaction rapidly without inactivating the enzyme over an extended period.
Those and other objects of the present invention will become apparent from the description hereinafter.